Double grid electron tube and circuit



INVENTOR Hf//vz ax Y 'MTORNEY Jan. 5, 1937. H. Lux

` DOUBLE GRID ELECTRON TUBE AND CIRCUIT Filed Nov. 16, 1932 PatentedJan. 5, i937 UNITED DOUBLE GRID ELECTRON TUBE AND CIRCUIT GermanyApplication November 16, 1932, Serial No. 642,845 In Germany November17, 1931 Claims.

In the methods discovered by Barkhausen and Kurz for producingoscillations by means of braking fields, the electrons, as is known,perform pendulum movements around the highly positive 5 grid of a 3electrode tube in which the anode has the potential of the cathode or aweak negative voltage. The electrons emitted by the iilamentparticipate,` if they are not effected by particular measures, only tothe smallest extent in the pendulummovements, whereas the major amountof electrons are moving in a straight line towards the grid where theyproduce heat and thereby limit the loading capacity of the tube. Theproportion between the grid losses and the oscillat- 16 ing power isabout 100:1. An explanation for this phenomenon can be found whenconsidering the electric field between grid and filament, the shape ofwhich is shown in Figure 1. All of the electrons which enter thestraight or only slightly curved fields will move to the grid in astraight line. Only at such places where the lines of force have aconsiderable curvature, the electrons do not follow the latter butmaintain, due to their mass inertia, the straight path and then carryout the desired pendulum movements.

The object of the present invention is to provide such fielddistribution so as to possibly avoid straight lines of force extendingbetween the grid and the filament. As a result a larger portion of theemitted electrons is caused to carry out pendulum movements and thesupply of nonoscillating electrons to the grid is reduced. This causes adecrease of the grid load and alsov an increase of the grid potentialwhich in turn enables a decrease of the wave length.

In the drawing Fig. 1 illustrates diagrammatically the electric iieldbetween the several electrodes of a three-electrode tube. Fig. 2illustrates diagrammatically a four-electrode tube according to thepresent invention, and the electric field between the electrodesthereof. Fig. 3 illustrates a practical embodiment of the tube shown inFig. 2 in connection with either a transmitting circuit or a receivingcircuit. Fig. 4 is a detail view showing schematically the relation ofone form of a pair of grids according to the invention, and Fig. 5 is atransverse sectional view showing the relation of another form of a pairof grids according to the invention.

In order to obtain the desired eld distribution it is suggested toprovide for instance a second grid between the filament and the positivegrid electrode. In Figure 2 the iilament is shown as I, the positivegrid is shown as at 2 and the (Cl. Z50-36) anode of a 3-electrode tubeis designated at 3. The wires of the second grid l! must be arranged insuch manner so as to be on a straight line through grid 2 perpendicularwith respect to anode 3 and lament I. When a spiral shaped grid isprovided, two helices are obtained (Fig. 4) which are of equal pitch butof a dilferent diameter and the wires as such determine an orthogonalscrew surface. Where a rod shaped grid is used, as shown in Fig. 5, thesingle rods must be in the same radial plane. When these requirementsare fullled the eld distribution follows the course shown in dottedlines in Figure 2. A deviation from this required arrangement wouldhowever be of detrimental eiect to a tube, as compared with a tubehaving only one grid. The grid 4 may either be connected to the cathode,or may have a negative potential applied to it. It will chargenegatively as a free grid and thus also fuliill its purpose.

In order to prevent the electrons from directly impinging upon the grida screen may be provided composed of dielectric materials such as mica,glass or quartz whereby the shape must be in accordance with the sameprinciple as reierred to above in connection with a metallic screengrid.

The manner in which my improved double grid tube may be used in atransmitter is illustrated in Figure 3. Modulating audio frequencypotentials from microphone 5 and audio frequency amplier 6 are appliedto the anode 8 through the transformer Ill. The secondary of transformerHl is connected in series with the lead I2 maintaining the anode at ahighly or slightly negative potential with respect to the filament lewhich is energized to an electron emitting condition by the action ofheater battery I6 and lament voltage adjusting resistor I8.

The grid 20 through which the electrons make their pendulum-likemovements is maintained at a highly positive potential by the action ofsource 2| applying a positive voltage to it through lead 22. Chokes 2liare provided to prevent undesired iow of high frequency current in thepolarizing leads and sources.

The added grid 26 according to my present invention is maintained eitherat lament potential or at a slightly negative potential by the suitabletapping of lead 28 on to negative biasing source 30 or directly on tothe lament lead 32. Oscillatory energy will then be developed in theLecher wire system 30 tuned by the action of short circuiting condenser32. A transmission line 34 may then be coupled to the Lecher wire systemas shown so as to suitably load the same and feed into a radiatingantenna 36.

Modulation is effected by virtue of variation in plate potential due tothe action of transformer Ill in series with the plate 8. If desired,the secondary of the transformer I may be inserted with similar effectin the lead 28 for the negatively maintained grid or grounded grid, or,

section, the cross-sections will be in similar alignment as indicated inFigure 4.. In the event that a rod-like structure is used for grids, asshown in Fig. 5, the rods 26 and 20 of the respective grids should bearranged so that they lie in cross-section upon the same radial linerunning through the cylindrical cathode or lament.

If desired, as already indicated, the inner grid 26 may be left oating,in which case electrons impinging thereon will give it the desirednegative polarization.

Also, my improved tube may be used in a receiving system in which caseantenna 36 would be a receiving antenna and the voltages and Lecher wiresystem 30 would be so adjusted that the tube would produce oscillationsat the frequency of the incoming waves. Hence, by virtue of an autodyneeffect audio frequency energy may be derived from transformer I 0amplified by an laudio frequency amplifier 6 and fed to a suitabletranslating device or loudspeaker 5. Here also, the transformer Il] maybe placed in series with the other gridv 26, or in series with thepositively maintained grid 20. Also, for receiving, it is not necessarythat the oscillator oscillate at the mean frequency of the receivedWaves. The tube may be adjusted by means of the voltages applied and theLecher wire system to produce oscillations which will beat at a highfrequency with the incoming waves. In that event, transformer l0 wouldbe replaced by a radio frequency transformer and rectangle 6wouldindicateapparatus including a second oscillator and second detectoras well as, if desired, audio frequency amplifiers for actuatingloudspeaker 5. Here also the radio frequency transformer l0 may beplaced, if desired, in series with the inner grid 26 or outer grid 2U.

What I claim is:

1. In a system for the production of high frequency oscillations, anelectron discharge tube including a cathode, a grid having portionsopaque to the passage of electrons and portions which permit the flow ofelectrons therethrough, an anode surrounding the grid, means forapplying to the grid a positive potential with respect to the cathode,means for applying to the anode a materially lower potential wherebyelectrons will oscillate back and forth between said cathode and anodethrough said grid, and means for reducing the impingement of electronsupon the opaque portions of said grid and thereby the losses in saidsystem, comprising an electrode similar to said grid and interposedbetween the grid and the cathode, said electrode having opaque portionsaligned with those of the grid, said electrode having applied thereto apotential of the order of the cathode whereby the number of straightlines of force between the grid and the cathode is materially reduced. Y

2. In an oscillating system of the Barkhausen- Kurz type, an electrondischarge tube comprising a cathode, an anode, a first grid electrodeadjacent the anode, means for applying to said grid electrode a positivepotential with respect to the cathode, a second grid electrodeinterposed between the cathode and the first grid electrode, and meansforY applying to said second grid and to the anode potentials ofsubstantially the same order of magnitude but materiallylowerthan thatlapplied to the rst grid.

3. In an oscillating system of the Barkhausen- Kurz type, an electrondischarge tube comprising a cathode, an anode, a first grid electrodeAadjacent the anode, means for -applying to said grid electrode apositive potentialfwith respect to the cathode, a second grid electrodeinterposed between the cathode and the rst grid electrode, and means forapplying to said second grid andtor the anode potentials ofsubstantially the same order of magnitude but materiallylower than thatapplied to the first grid, said grid electrodes being so arranged 1thatA theperforations of one are parallel and in alignment with theperforations of the other.

4. In an oscillating system of 'the Barkhausen- Kurz type, an electrondischarge tube comprising i a cathode, an anode, a grid electrodeadjacent the anode, means Yfor applying to said grid` elec'- trode apositive potential with respect to lthe cathode, a second grid electrodeinterposed be- L,

tween the cathode and the rst Ygrid electrode, and means for applying anegative potential with respect to the cathode to both the second gridelectrode and the anode.

5. In an oscillating system of the Barkhausen* Kurz type, an electron`discharge tube compris-v ing a cathode, an anode,` a first gridelectrode 'Y adjacent the anode, means for applyingto said gridelectrode a positive potential with respect to the cathode, a secondkgrid electrode interposed bef7

